1. Field of the Invention
This invention relates to low molecular weight, non-peptidic, non-peptidomimetic, organic molecules that act as modulators of mammalian complement C5a receptors, preferably ones that act as high affinity C5a recptor ligands. The invention also relates to such ligands that act as antagonists (including inverse agonists) of complement C5a receptors, preferably human C5a receptors. This invention also relates to pharmaceutical compositions comprising such compounds. It further relates to the use of such compounds in treating a variety of inflammatory and immune system disorders. Additionally, this invention relates to the use such compounds as probes for the localization of C5a receptors.
2. Background of the Invention
C5a, a 74 amino acid peptide, is generated in the complement cascade by the cleavage of the complement protein C5 by the complement C5 convertase enzyme. C5a has both anaphylatoxic (e.g., bronchoconstricting and vascular spasmogenic) and chemotactic effects. Therefore, it is active in engendering both the vascular and cellular phases of inflammatory responses. Because it is a plasma protein and, therefore, generally almost instantly available at a site of an inciting stimulus, it is a key mediator in terms of initiating the complex series of events that results in augmentation and amplification of an initial inflammatory stimulus. The anaphylatoxic and chemotactic effects of the C5a peptide are believed to be mediated through its interation with the C5a receptor (CD88 antigen), a 52 kD membrane bound G-protein coupled receptor (GPCR). C5a is a potent chemoattractant for polymorphonuclear leukocytes, bringing neutrophils, basophils, eosinophils and monocytes to sites of inflammation and/or cellular injury. C5a is one of the most potent chemotactic agents known for a wide variety of inflammatory cell types. C5a also xe2x80x9cprimesxe2x80x9d or prepares neutrophils for various antibacterial functions, e.g., phagocytosis. Additionally, C5a stimulates the release of inflammatory mediators (e.g., histamines, TNF-xcex1, IL-1, IL-6, IL-8, prostaglandins, and leukotrienes) and the release of lysosomal enzymes and other cytotoxic components from granulocytes. Among its other actions, C5a also promotes the production of activated oxygen radicals and the contraction of smooth muscle.
Considerable experimental evidence implicates increased levels of C5a in a number of autoimmune diseases and inflammatory and related disorders.
Antagonists that block the binding of C5a to its receptor or other agents, including inverse agonists, which modulate signal transduction associated with C5a-receptor interactions, can inhibit the pathogenic events, including chemotaxis, associated with anaphylatoxin activity contributing to such inflammatory and autoimmune conditions. Despite many attempts, no one has previously been able to provide any small molecule (less than 700 Daltons MW, or amu) non-peptide, non-peptidomimetic, non-peptoid, C5a antagonist that is essentially free of agonist activity at the C5a receptor and that exhibits a binding affinity for the C5a receptor of less than 1 micromolar, and preferably less than 100 nanomolar.
Certain modified C5a peptides (i.e., modifications of C5a) have been identified as partial C5a antagonists and have been shown to block a number of C5a mediated actions including neutrophil chemotaxis, neutropenia and superoxide formation. Various C5a peptidomimetic compounds have also been reported as modulating C5a activity, including cyclic peptoids (a peptoid is a peptidomimetic compound comprising an oligomeric assemblage of naturally occurring amino acids that have been N-substituted). Typically these C5a modulatory compounds exhibit a molecular weight greater than 500 Daltons, and generally greater than 700 Daltons.
The present invention provides novel compounds that are small molecule C5a receptor antagonists that are non-peptide, non-peptidomimetic, and are preferably free of C5a receptor agonist activity, which compounds exhibit high affinity for the C5a receptor, i.e., an affinity constant for binding to the C5a receptor of less than 1 micromolar. Highly preferred compounds exhibit very high affinity for the C5a receptor, i.e., an affinity constant for binding to the C5a receptor of less than 100 nanomolar.
Preferred compounds are C5a receptor antagonists (including inverse agonists).
Preferred antagonists exhibit an antagonist EC50 (which as usd herein includes IC50) of less than 1 micromolar, preferably less than 100 nanomolar, in an assay of C5a mediated chemotaxis. Preferred C5a receptors are mammalian, preferably primate receptors, including human C5a receptors, and may either be cloned, recombinantly expressed receptors or naturally expressed receptors. In certain preferred embodiments, compounds of the invention exhibit an affinity for human C5a receptors that is higher than for rodent C5a receptors, preferably at least five times higher, more preferably ten times higher.
The compounds of the present invention do not interact with dopamine receptors with even moderate affinity, i.e., they do not bind to dopamine receptors with Ki values of less than 100 micromolar. Preferred compounds of the invention do not bind to any naturally occurring receptors other than C5a receptors with high affinity, and preferably they do not bind to any naturally occurring receptors other than C5a receptors with even moderate affinity.
In certain embodiments these compounds also possess one or more, and preferably two or more, three or more, four or more, or all of the following properties in that they are: 1) multi-aryl in structure (having a plurality of un-fused or fused aryl groups), 2) heteroaryl in structure, 3) orally available in vivo (such that a sub-lethal or preferably a pharmaceutically acceptable oral dose can provide a detectable in vivo effect such as a reduction of C5a-induced neutropenia), 4) comprised of fewer than four, preferably fewer than three, or fewer than two, or no amide bonds, and 5) capable of inhibiting leukocyte chemotaxis at nanomolar concentrations and preferably at sub-nanomolar concentrations.
In a highly preferred aspect, the invention provides non-peptidic, non-peptidomimetic, low molecular weight compounds that act as high affinity antagonists of the human C5a receptor. Specifically exemplified representative compounds include, but are not limited to optionally substituted arylimidazoles (i.e. imidazoles having one or more ring substituents of optionally substituted carbocyclic aryl or optionally substituted heteroaryl), optionally substituted arylpyridyls (i.e. pyridyls having one or more ring substituents of optionally substituted carbocyclic aryl or optionally substituted heteroaryl), optionally substituted aryl-substituted cycloalkylimidazoles (i.e. cycloalkylimidazoles having one or more ring substituents of optionally substituted carbocyclic aryl or optionally substituted heteroaryl), optionally substituted arylpyrazoles (i.e. pyrazoles having one or more ring substituents of optionally substituted carbocyclic aryl or optionally substituted heteroaryl), optionally substituted benzimidazoles, optionally substituted aryl-substituted tetrahydroisoquinolines (i.e. tetrahydroisoquinolines having one or more ring substituents of optionally substituted carbocyclic aryl or optionally substituted heteroaryl), and optionally substituted biaryl carboxamides (i.e. a carboxamide that has one or more optionally substituted bi-carboxylic aryl or heteroaryl substituents). Novel intermediates useful for synthesizing compounds of the invention are also provided.
Preferred compounds of the invention are compounds of Formula I, shown below, that bind specifically, and preferably with high affinity, to C5a receptors.
The invention also provides pharmaceutical compositions comprising compounds of the invention, including those of Formula I, including otppinally substituted arylimidazoles, optionally substituted arylpyridyls, optionally substituted aryl-substituted cycloalkylimidazoles, optionally substituted arylpyrazoles, optionally substituted benzimidazoles, optionally substituted aryl-substituted tetrahydroisoquinolines, and optionally substituted biaryl carboxamides. The C5a receptor antagonist compounds described herein are particularly useful in the treatment of C5a-mediated inflammation, e.g., inflammation associated with various inflammatory and immune system disorders. The invention further comprises a method of treating a patient in need of such anti-inflammatory treatment or immune treatment an effective amount of a compound of the invention, e.g. an amount of a compound of the invention sufficient to yield a plasma concentration of the compound (or its active metabolite, if a pro-drug) high enough to inhibit white blood cell (e.g., neutrophil) chemotaxis in vitro. Treatment of humans, domesticated companion animals (pets) or livestock animals suffering such conditions with an effective amount of a compound of the invention is contemplated by the invention. For treating non-human animals of any particular species, a compound exhibiting high affinity for the C5a receptor of that particular species is preferred.
In a separate aspect, the invention provides methods of using compounds of the invention as positive controls in assays for receptor activity and using appropriately labeled compounds of the invention as probes for the localization of receptors, particularly C5a receptors, e.g., in tissue sections (e.g., via autoradiography) or in vivo (e.g., via positron emission tomography, PET, or single positron emission computed tomography, SPECT, scanning and imaging).
The invention provides compounds and compositions that are useful as inhibitors of C5a-mediated chemotaxis (e.g., they may be used as standards in assays of such chemotaxis). The invention additionally comprises methods of inhibiting C5a-mediated cellular chemotaxis, preferably leukocyte (e.g., neutrophil) chemotaxis. These methods comprise contacting white blood cells, particularly primate white blood cells, especially human white blood cells, with one or more compounds of the invention. Preferably the concentration is sufficient to inhibit chemotaxis of white blood cells in an in vitro chemotaxis assay, so that the levels of chemotaxis observed in a control assay (e.g., one to which a compound of the invention has not been added) are significantly higher (significantly here measured as pxe2x89xa60.05 using a conventional parametric statistical analysis method such as a student""s T-test) than the levels observed in an assay to which a compound of the invention has been added.
Accordingly, a broad aspect of the invention is directed to non-peptidic organic (carbon-containing) molecules, having a molecular mass of less than 700 amu, that exhibit C5a antagonist activity or C5a inverse agonist activity with an EC50 of less than 500 nM in an assay of C5a mediated leukocyte chemotaxis.
More particularly the invention includes compounds of Formula I, 
wherein:
AR1 and AR2 are independently carbocyclic aryl or heteroaryl;
LIP represents an alkyl, carbocyclic aryl, heteroaryl, or arylalkyl;
A is oxygen or nitrogen;
d1 represents the distance between A and the geometric center of AR1 and is between 3 and 6 angstroms in at least one energetically accessible conformer of the compound;
d2 represents the distance between A and the geometric center of AR2 and is between 5 and 10 angstroms in at least one energetically accessible conformer of the compound; and
d3 represents the distance between A and the nearest atom of LIP and is between 3 and 6 angstroms in at least one energetically accessible conformer of the compound.
Preferred compounds of Formula I exhibit antagonist (including inverse agonist) activity at C5a Receptors, and essentially no or little agonist activity at this receptor. Preferably such compounds contain one or more heteroaryl rings.
Preferred compounds of the invention exhibit good activity in standard in vitro C5 receptor mediated chemotaxis assay, specifically the assay as specified in Example 12, which follows and is defined below. Alternative preferred assays include the calcium mobilization assay. Preferred compounds of the invention exhibit an EC50 of about 500 nM or less in such a standard C5a mediated chemotaxis assay, more preferably an EC50 of about 200 nM or less in such a standard C5a mediated chemotaxis assay, still more preferably an EC50 of about 100, 50, 25 and 10 nM in such a standard C5a mediated chemotaxis assay, even more preferably an EC50 of about 5 nM in such a standard C5a mediated chemotaxis assay.
The invention includes additional methods such as methods for localizing C5a recerptors in tissue section samples, comprising cotacting a tissue sample with detectably labelled one or more compounds of the invention that are preferably detectably labeled, optionally washing the contacted tissue sample, and detecting the bound compound associated with the tissue sample. Suitable detectable labels include e.g. 125I, tritium, 32P, 99Tc or the like. A variety of detection methods could be employed include single emission photono computed tomography (xe2x80x9cSPECTxe2x80x9d).
Other aspects of the invention are discussed infra.